Whatever you think of Tony Blair, one charge that surely cannot be levelled against his memoir, A Journey, is that it wants for frankness or thoroughness. Over its 700 pages, the former prime minister touches on just about every aspect of his political career, and much besides, in far more detail than he could possibly have got away with while still in office. His relationship with Gordon Brown; Iraq; his views on the economic crisis; Cherie and the family; the importance of privacy in the bathroom – all receive the treatment.

But there is one area – one rather close to home – where a self-denying ordinance remains. ‘I love the Labour party,’ Blair tells us, happy to talk in broad terms about the party he led for 13 years. But he has resolutely refused to endorse a candidate for leader. He is widely assumed to be backing David Miliband, and says nothing during our interview that suggests otherwise.

‘I wouldn’t presume to give [the next leader] advice,’ Blair says. But while ‘it’s going to be a very tough job,’ the next general election is ‘completely winnable.’

‘Politics is in an era of low predictability and there’s every opportunity for Labour not to conform to the usual trend, which is that once it loses it goes into a long period of opposition, but to say, “no, we’re going to get straight back into contention as a governing party.” But that requires the mentality and the psychology of government.’

Blair argues that this is, in part, about Labour being institutionally shipshape.

‘[Labour] mustn’t go back to old ways of organising because that is hopeless in today’s world. You’ve got to organise people and parties in a completely different way if you want to succeed today. You look around the world – whether it is Obama on the left, or actually, Sarkozy on the right – the parties that win, do it differently.’

David Miliband’s Movement for Change, which is training up 1,000 community organisers to ‘rebuild the Labour movement from the bottom up’, immediately springs to mind. Yet the New Labour project always had more to do with political style – the importance of challenging the Labour party to move out of its ‘comfort zone’ – and with policies such as public service reform. Here, Blair says much that is interesting and suggestive.

Asked what he thinks of the Tories’ attempt to spin A Journey as an endorsement of their policies to cut the fiscal deficit this year and to raise VAT, Blair says, ‘I would probably have taken the way that I think that Alistair Darling wanted to get out of the crisis, and that’s what I support … The problem for the left is that [it] always has this idea that the state is back in fashion … What we should have realised is that at the moment of the financial crisis … everyone [had] to take tough medicine, and in fact the state should have been taking tough medicine, too.’

Darling said recently that he wanted to raise VAT before the election, but was overruled by Gordon Brown. Darling also authored Labour’s commitment to halve the deficit within four years. Of the leadership candidates, David Miliband has been by far the most explicit in expressing his desire to retain this pledge and Blair clearly sees it as a touchstone issue on which the party – and most of the leadership candidates – must be challenged.

‘My view is that you never let the Tories own policy … it is important to have the debate in the Labour party … I grew up in a situation in the Labour party where for years we weren’t taking the right decisions because everyone said, “Let’s unify!” And I always used to say people, “no, let’s have the debate first – then unify”. You can conduct this reasonably, incidentally. You don’t have to hate each other or disrespect each other. Because if you don’t have the debate, and you just unify, if you’re not careful you unify in your comfort zone, which may be fine and keep you very comfortable and you really like being there, and then it comes to a general election and you find you can’t win.’

It’s difficult to interpret this as anything other than a rebuke to Ed Miliband and to some extent Andy Burnham, both of whom have criticised New Labour’s style of politics: Miliband inverted Blair’s phrase by seeking to move away from ‘the New Labour comfort zone’, while Burnham decried ‘New Labour elitism.’

In mapping out where he thinks Brown went wrong – and, by implication, where the next leader can pull things round – Blair remains unrepentantly wedded to the project.

‘I was always very clearly of the view that a genuine renewal of New Labour was not going back into the comfort zone but advancing even further outside it. If we’d done that … there was no reason why we had to lose the last election and I think that’s very important to recognise.’

Asked where he would have taken New Labour next, Blair mentions the need for ‘a strategic and empowering state’, welfare reform, more academy schools, ‘and I would have taken the whole law and order thing and gone a lot further’.

Hardly music to the ears of many Labour members, one imagines. These, significantly, are exactly the sort of knotty issues either left untouched by the party leadership candidates, or, like ID cards, repudiated by them. Blair argues that you cannot talk about immigration – much discussed by the leadership candidates – without talking about identity cards.

‘The issue is not immigration, the issue is illegal immigration … You can always control legal immigration – you decide what the law is. The problem is illegal immigration and the only way of dealing with it is identity cards,’ says the former prime minister.

Given Brown’s perceived missteps – and Blair’s evident impatience with the tenor of the debate surrounding the leadership contest – we ask whether he regrets not doing more to ensure that there was a New Labour challenger to Brown before he acceded to No 10 in 2007.

‘Well, when the so-called coup happened in September 2006, I didn’t leave for nine months, so someone could have come forward,’ he says. ‘But people forget now, there was a huge party and media consensus for Gordon and for perfectly sensible reasons: he was a colossal figure and, as I keep saying, made an enormous contribution to the government.

‘I know some people think I have been very tough on him in the book but actually you can’t write the 10 years without writing about it, and I have been simply frank that there was a policy disagreement in the end and that that policy disagreement – the reason it is important to write about it – is that that issue is still there for us today.’

This is the closest Blair comes to suggesting that although he thinks it politic to stay out of the leadership election, he’s finding getting involved pretty near irresistible. And the lesson Blair wants to convey is a familiar one – that, in the final analysis, Labour can achieve nothing if it does not win, and it will not win if it is not New Labour.

‘For 100 years, we couldn’t win two successive full terms …we’ve won three now. Maybe it had nothing to do with the concept of New Labour. But just possibly it might!’